Composite contactor roll for electroplating

ABSTRACT

A composite roll comprises a shell of nickel alloy and a steel sleeve within the shell. The sleeve is in contact with the middle portion of the shell and out of contact with the end portions of the shell. An annulus of elastomer is disposed between the end portions of the shell and the sleeve. A collector head is secured to each end of the roll.

United States Patent 1191 Weiskopf Jan. 14, 1975 COMPOSITE CONTACTOR ROLL FOR 2,666,347 12/1941 Watson 19m A ELECTROPLATING 3,678,226 7/1972 Hatagi l9l/l A [75] Inventor: Daniel A. Weiskopf, Bethlehem, Pa.

[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

[22] Filed: May 18, 1973 [21] Appl. No.: 361,680

[52] U.S. Cl 191/1 A [51] Int. Cl B60l 9/00 [58] Field of Search 191/1 A [56] References Cited UNITED STATES PATENTS 2,513,515 7/1950 Powers l9l/1A Primary ExaminerM. Henson Wood, Jr.

Assistant ExaminerD. W. Keen Attorney, Agent, or Firm-Joseph J. OKeefe; John 1. Iverson; Robert M. Jones [57] ABSTRACT A composite roll comprises a shell of nickel alloy and a steel sleeve within the shell. The sleeve is in contact with the middle portion of the shell and out of contact with the end portions of the shell. An annulus of elastomer is disposed between the end portions of the shell and the sleeve. A collector'head is secured to each end of the roll.

5 Claims, 3 Drawing Figures COMPOSITE CONTACTOR ROLL FOR ELECTROPLATING BACKGROUND OF THE INVENTION This invention relates to electroplating, and morev particularly to a composite contactor roll for use in acid electroplating baths.

Metal, e.g., steel, strip may be coated by passing the strip through a plurality of tanks containing anodes of the coating material, e.g., tin, disposed in an electrolyte. The strip is pulled along the surface of the bath by a plurality of sets of rolls, each set comprising an upper, electrically conductive contactor roll and a lower, electrically non-conductive back-up roll.

Contactor rolls in the past were generally made of steel, which is a highly conductive metal. Steel rolls, however, were subjected to chemical attack by certain electrolytes, e.g., tin fluorides and chromic acid. In addition, the coating metal electrodeposited on the contactor roll at the junctions of the edges of the strip and the contactor roll, causing arcing and consequent strip damage, as well as high operating costs due to the need for periodic dressing of the roll surface and the operating delays associated therewith.

In view of the foregoing, attempts have been made to provide contactor rolls having propertieswhich are superior to those of steel rolls insofar as these problems are concerned. One such roll, shown and described in U.S. Pat. No. 2,266,347 to Watson l94l, comprised a shell of acid-resistant metal, e.g., nickel, mounted on an axle by means of steel end plates fitted within the ends of the shell. Because nickel is characterized by only medium electrical conductivity, a plurality of axially disposed copper bars were sweated to the inside of the shell and passed through openings in the steel end plates into contact with a copper disc, or collector head, contiguous to each steel end plate. Each disc was then connected to a source of current.

The Watson contactor roll, while being superior to the prior steel rolls in its resistance to chemical attack, proved to be far worse in its resistance to electrodeposition of coating metal on the roll itself, particularly at the ends thereof.

Another prior art contactor roll, shown and described in U.S. Pat. No. 2,513,515 to Powers 1950, comprised a conductive metal mid-portion having electrically non-conductive, e.g., neoprene, sleeves on either side thereof. The metal mid-portion was adapted to engage the metal to be plated intermediate its side edges.

The Powers contactor roll was incapable of handling a wide range of strip widths, e.g., 20 inches to 48 inches, since for a wide strip the very large amount of strip overlapping the neoprene portion of the roll will have a significantly smaller quantity of electrodeposited metal thereon than will that portion of the strip passing over the highly conductive metal mid-portion. In addition, because the pressure between the contactor roll and the back-up roll must be about 60 to 80 psi. to overcome the hydraulic wedge effect of solution carried by the strip, the strip tended to crease at the juncture of the metal mid-portion and the neoprene side portions. Excessive plating metal collaring at the juncture also occurred because of either disbonding of plated metal or the occurrence of wear grooves at the BRIEF SUMMARY OF THE INVENTION I have discovered that the foregoing object can be obtained by providing a roll having an impedance path from its surface to the collector heads at the ends thereof which is medium at its middle portion and relatively high at its end portions, although said high impedance is much less than that characteristic of a dielectric. To this end I provide a composite roll comprising a cylindrical shell which, in addition to having high resistance to chemical attack by the electroplating bath, is characterized by medium electrical resistivity. A cylindrical body is disposed within said shell in contact with the middle portion of the shell and out of contact with the end portions thereof, said body being characterized by a resistivity substantially lower than that of said shell. Annular electrical insulating means is disposed between the end portions of said shell and said cylindrical body. Means, including a collector head secured to each end of said roll, provides a low resistance path from said cylindrical body to a source of current.

By reason of the foregoing construction, the composite roll of the invention is characterized by a high resistance to chemical attack by the electroplating bath. In

addition, the annular insulating means of the roll, in

combination with the medium electrical resistivity of the shell, presents a high impedance path at the ends of the roll and immediately adjacent thereto, thereby substantially eliminating electrodeposition of coating metal in this region. The provisions of a shell of medium resistivity, in combination with a cylindrical body therewithin having a relatively low resistivity, results in only a minor amount of electrodeposition of coating metal at the juncture of the strip edges and the roll face.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view, partly in section, of one embodiment of the invention.

FIG. 2 is a sectional view through the lines 2-2 of FIG. 1.

FIG. 3 is a sectional view through the lines 33 of FIG. 1.

FIG. 4 is a side elevation view, partly in section, of another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1, 2 and 3, the roll of the invention broadly comprises a cylindrical shell 10 of a material having high resistance to chemical attack by the electroplating bath, e.g., a conventional halogen tin plating bath comprising primarily tin fluorides. The shell is formed of a nickel alloy, preferably Hastelloy C, which has medium electrical resistivity e.g., about 780 ohm circular-mils/foot. The composition of Hastelloy C is, by weight, 54% nickel, 17% molybdenum, 15% chromium, 5% iron, and 4% tungsten.

The shell 10 is secured to a sleeve 12 having a resistivity substantially lower than that of Hastelloy C, e.g., carbon steel, which has a resistivity of about -130 ohm-circular-mils/foot. The shell is preferably shrink-fitted onto the sleeve 12 and is coaxial therewith. The sleeve 12 is in contact with the middle portion of the shell, the end portions of the sleeve being machined to a lesser diameter than that of its midsection. The resultant annular openings between the sleeve and the end portions of the shell are provided with electrical insulation 16, e. g., a dielectric elastomer such as chlorosulfonated polyethylene. Alternatively, the annular openings may simply be plugged with an elastomer seal at the ends thereof. Secured to each end of the sleeve 12 is a collector head 18, said head 18 being formed of copper and adapted to be connected to a source of current. In one example of the invention, a 60 inch roll was provided with insulation extending 12 inches inwardly of each end of the roll, and was used successfully in tin plating strip of widths throughout the range of 20 to 48 inches.

As shown in FIG. 4, the roll of the invention may comprise a shell 20 of nickel alloy metallurgically bonded to an inner sleeve of copper intermediate the ends of the shell. The shell 20 and sleeve 22 were then shrink fitted onto a solid steel roll core 24, and the spaces between the core 24 and the shell 20 filled with an electrical insulating elastomer 26. In this instance, the core itself also serves as the collector head for the current.

I claim:

1. A composite roll for use in pulling a strip through a bath of liquid, comprising:

a. a cylindrical shell characterized by high resistance to chemical attack by said liquid and by medium electrical resistivity;

b. a cylindrical body within said shell, said body being in contact with the middle portion of said shell and out of contact with the end portions thereof, said body being characterized'by a resistivity substantially lower than that of said shell;

0. means, including a collector head secured to each end of said roll, providing a low resistance path from said cylindrical body to a source of current; and g d. annular electrical insulating means disposed in contact with the inner surfaces of the end portions of said shell, said insulating means combining with said shell to provide said roll with an impedance path from the roll surface to said collector head at each end portion of said roll which is high relative to the corresponding impedance path at the middle portion of said roll.

2. A roll as recited in claim 1, in which said shell is a nickel alloy, said cylindrical body is steel, and said electrical insulating means is an elastomer.

3. A roll as recited in claim 1, in which said annular electrical insulating means is in contact with the entire inner surfaces of the end portions of said shell.

4. A roll as recited in claim 1, in which said electrical insulating means comprises an elastomer.

5. A composite roll for use in apparatus for continuously electroplating steel strip, comprising:

a.- a cylindrical metal shell, said shell being characterized by high resistance to chemical attack by the electroplating bath and by medium electrical resistivity;

b. a metal sleeve within said shell, said sleeve being in contact with the middle portion of said shell and out of contact with the end portions thereof, said sleeve being characterized by a resistivitysubstantially lower than that of said shell;

c. annular electrical insulating means disposed between the end portions of said shell and said sleeve, said means comprising an elastomer; and

d. means, including a collector head secured to each end of said roll, providing a low resistance path from said sleeve to a source of current. 

1. A composite roll for use in pulling a strip through a bath of liquid, comprising: a. a cylindrical shell characterized by high resistance to chemical attack by said liquid and by medium electrical resistivity; b. a cylindrical body within said shell, said body being in contact with the middle portion of said shell and out of contact with the end portions thereof, said body being characterized by a resistivity substantially lower than that of said shell; c. means, including a collector head secured to each end of said roll, providing a low resistance path from said cylindrical body to a source of current; and d. annular electrical insulating means disposed in contact with the inner surfaces of the end portions of said shell, said insulating means combining with said shell to provide said roll with an impedance path from the roll surface to said collector head at each end portion of said roll which is high relative to the corresponding impedance path at the middle portion of said roll.
 2. A roll as recited in claim 1, in which said shell is a nickel alloy, said cylindrical body is steel, and said electrical insulating means is an elastomer.
 3. A roll as recited in claim 1, in which said annular electrical insulating means is in contact with the entire inner surfaces of the end portions of said shell.
 4. A roll as recited in claim 1, in which said electrical insulating means comprises an elastomer.
 5. A composite roll for use in spparatus for continuously electroplating steel strip, comprising: a. a cylindrical metal shell, said shell being characterized by high resistance to chemical attack by the electroplating bath and by medium electrical resistivity; b. a metal sleeve within said shell, said sleeve being in contact with the middle portion of said shell and out of contact with the end portions thereof, said sleeve being characterized by a resistivity substantially lower than that of said shell; c. annular electrical insulating means disposed between the end portions of said shell and said sleeve, said means comprising an elastomer; and d. means, including a collector head secured to each end of said roll, providing a low resistance path from said sleeve to a source of current. 